It is a real crackpot that would be a trapeze artist (9)
I believe the answer is:
aerialist
'a trapeze artist' is the definition.
(someone doing acrobatics on a trapeze)
'it is a real crackpot' is the wordplay.
'crackpot' indicates an anagram (I've seen this in other clues).
'it'+'is'+'a'+'real'='itisareal'
'itisareal' anagrammed gives 'AERIALIST'.
'that would be' is the link.
(Other definitions for aerialist that I've seen before include "Highly-regarded performer" , "skier" , "trapeze artist" , "Trapeze acrobat" .)